Critical behaviour of second sound near the smectic A nematic phase transition

Abstract

We show that the smectic A compressional elastic constant, measured in the (100 kHz, q ≃ a few 102 cm-1) range exhibits a critical behaviour consistent with either the helium analogy (8 CB) or the proximity of a tricritical point (8 OCB). The extreme anisotropy of the second sound propagation velocity is also established in a range not accessible previously